The present invention relates to imaging systems and, more particularly, to techniques for detecting and responding to a plurality of interrupts occurring in real time.
Modern imaging systems such as, for example, X-ray imaging systems, are operated under control of a digital computer for performing a complex sequence of control activities required to produce a desired image while minimizing human exposure to X radiation and avoiding damaging operating parameters on the X-ray equipment. The imaging modes may be, for example, simple two-dimensional exposure, computer axial tomographic three-dimensional exposure, or cine exposure. Each of these modes requires a different control sequence. Preferably, operation of the imaging equipment is changeable from mode to mode upon an operator's command.
In one type of X-ray imaging equipment, the sequence of operations is controlled by recipes detailing the activities required and the preconditions enabling advance to a subsequent activity. For example, before an X-ray tube is called on to produce radiation, confirmation is required that its voltages are at predetermined levels and that its anode rotation apparatus is up to speed.
Data representing commands and data representing responses of the system to the commands or external conditions is transmitted between system elements on a high-speed parallel data bus. Some of the data items are of such importance that they require immediate attention by the system. Such important data must be recognized by the system for the generation of an interrupt. In response to the interrupt, the central processor pauses its current task to pursue the higher-priority task represented by the interrupt. Once the higher-priority task is completed, the processor may return to the interrupted task or, in some instances, it may be commanded to jump to a completely different task, abandoning the original task.
In order to sense the data conditions requiring an interrupt, the parallel data bus is sampled at a frequency high enough to attain the required responsiveness. One of the problems the present invention addresses is a technique for attaining the required responsiveness without excessive cost.
A system condition capable of generating an interrupt in one mode may be irrelevant in a different mode or different portion of the same mode. Thus, data patterns on the parallel data bus are necessarily passed through a sieve, or mask, which accepts for the generation of interrupts only those conditions relevant to the current mode of operation.